With some prediction a Rotom-W can have a field day with your team. You have a major Electric weakness bar Thundurus and other things like Celebi or Amoongus wont mind the HP Fire (HP Fire in rain...) Empoleon and Tentacruel are both Landorus weak who can spam a EQ or setup. Also once Sharpedo is gone you have a huge Chansey / Blissey weakness who wont mind the Focus Blast.

For Politoed make it a Bold nature to increase its defenses. I'd replace Empoleon with something like a Ferrothorn to take care of the Rotom-W weakness.

It can do everything that Empoleon can do without the Rotom-W weakness and Chansey and Blissey both hate Leech Seed. Even though Vaporeon is a excellent Wish passer a Cleric version with Rest / Heal Bell / Roar / Scald can also work. Seeing as Sharpedo already gets the Speed Boost I'd replace Aqua Jet with Earthquake to take down things like Jirachi. Interesting Tentacruel set even though I found that Toxic usually works over Toxic Spikes. Finally for Thundurus replace HP Fire for HP Ice.